1. Field of the Invention
The present invention relates generally to a surface decoration process, and more particularly to a method of molding a product with a surface film in a die.
2. Description of the Related Art
In the requirement of high precision and quality of plastic products, there are various surface decoration processes. For a process of attaching a surface film on a substrate in a die, the film is printed and decorated, and then is formed into a specific shape by high pressure gas and cut by a cutter to have a desired size. After that, the film is put in a die for injection molding. The product of injection molding has the film thereon to provide the function of wear-proof and durable texture or pattern. The film, however, is formed in different time before being put in the die so that the film may be not attached on a sidewall of a cavity of the die tightly because of its expansibility (or shrinkage) causing change of size or shape. Such condition may cause rupture of the film when molten plastic under high temperature and pressure is injected into the die. It causes shifting of texture or pattern on the products to increase the defect rate.
To fix above problem, an improved process, as shown in FIG. 1 to FIG. 5, was provided, which provides a die 1 with a first die member 2 and a second die member 3. The first die member 2 includes a first surface 2a and a protrusion 2b on the first surface 2a. The second die member 3 includes a second surface 3a and a recess 3b on the second surface 3a. The first step of the process is putting an elongated film 4 between the first die member 2 and the second die member 3 (the film 4 keeps a predetermined distance from the second die member 3). The second step is moving a heater 6 to a position above the film 4 and then moving it downward to press the film 4 onto the second surface 3a of the second die member 3. The heater 6 has a heating surface 6a against the film 4 to soften the film 4. A pump (not shown) is connected to the second die member 3 to suck air in the recess 3b out. As a result, the film 4 is sucked into the recess 3b and attached on a sidewall of the recess 3b. Next, moving the heater 6 out and moving the first die member 2 toward the second die member 3 with the protrusion 2b of the first die member 2 entering the recess 3b of the second die member 3. An injection molding process is performed to inject plastic onto the film 4. After that, the die 1 is opened to have a product with the film 4 thereon. The product with the film 4 thereon has no drawback as described above.
The product made by above method has the film 4 thereon for protection. The film 4 provides functions of wear-proof and preventing textures or pattern on the product from breaking or loosing. However, above method still has some drawbacks.
In the heating step, as shown in FIG. 2, the heater 6 almost touches the film that will melt the film 4. If the film 4 were not molten in the heating step, the heater 6 presses a margin of the film 4 in the following step, as shown in FIG. 3. In this moment, the film 4 is easy to be molten and the injection molding will be stopped when the film 4 is molten. Even though the film 4 can take the high temperature of the heater 6, it always warps by the changeable temperature of the heater 6 that makes a waved surface of the product and a bend angle of the product less than seventy degrees to narrow the applications of the product. In addition, the film 4 may be stuck on the heater 6 that the film 4 goes with the heater rather than on the second die member 3.
The injection molding process will be stopped when any problem as described above is occurred, and the process goes again when the problem has been fixed. It causes stop of manufacture and waste of materials. That is, above method still has to be improved.